Firing pressure activation system for fuzes and components



. June 17, 1969 I CQQKE ET AL FIRING PRESSURE ACTIVATION SYSTEM FOR FUZES AND COMPONENTS Filed Oct. 27, 1967 DETONATOR FIG. 6

FIG. 5

INVENTORS EDWARD A. COOKE WILLIAM H. CARTER ATTORNEYS.

United States Patent 3,450,046 FIRING PRESSURE ACTIVATION SYSTEM FOR FUZES AND COMPONENTS Edward A. Cooke, Mcleau, Va., and William H. Carter, White Plains, Md., assignors to the United States of America as represented by the Secretary of the Army Filed Oct. 27, 1967, Ser. No. 678,754 Int. Cl. F42c 15/32, 11/00, 1/00 US. Cl. 102-70.2 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a firing pressure activation system for fuzes and components and more particularly to a device suitable for use in arming the fare of a projectile. The present invention provides a ductile metal cup or a peripherally supported disc which is adapted to be dished inwardly by pressure developed behind the projectile by the propellant combustion gas when the projectile is fired. An abrupt increase in pressure causes the pressure hammer to move inwardly so as to bring a striker carried by the hammer into engagement with a conventional percusion primer or other type priming device responsive to high velocity impacts. The result is a simple, lightweight, very inexpensive, highly reliable and safe device particularly suited for activating base-mounted fuzes or other devices which relies for operation upon the propellant combustion pressure developed during firing of a projectile.

Deformable and movable devices responsive to combustion gas pressure have been proposed in the past for fuze systems. However, insofar as applicants are aware, the prior devices have all suffered from one or more serious disadvantages rendering them unsafe or not completely reliable for many fuze applications. In particular, previously proposed devices have been susceptible to actuation by a gradual buildup in pressure in or around the projectile as might be occasioned when the projectile was subjected to excessive heat. Since military weapons are not infrequently exposed to conditions of this type during fires, devices which may be actuated by gradual pressure buildup are considered unacceptable for many military applications. In addition, many of the prior devices lacked sulficient insensitivity to shock or Vibration.

The device of the present invention overcomes these and other diificulties by providing an extremely lightweight cup shaped or peripherally supported disc used in conjunction with a primer so that the system can only be actuated by abrupt, substantial increases in pressure. The pressure hammer may be drawn as a sheet metal cup or a punched sheet metal disc, is lightweight and is very cheap to produce. It is quite reliable in operation and repeated firings have resulted in no failure of the system to perform its required function. The device features very high safety protection since the unit is extremely insensitive (approaches immunity) to spurious initiation such as by shock or vibration and gradual increases in pressure will not cause it to operate inadvertently. It is particularly immune to pressure icnreases caused by heat resulting from fires and the round itself will be destroyed long 3,450,046 Patented June 17, 1969 before the system of this invention can be made to arm the fuze.

It is, therefore, one object of the invention to provide an improved firing pressure activation system for fuzes, fuze components, and similar devices.

Another object of the present invention is to provide a projectile arming device having improved safety due to its immunity to spurious initiation and high insensitivity to shock, vibration and heat.

Another object of the present invention is to provide a simplified and inexpensive arming device including a pressure hammer in the form of a small ductile metal cup or disc adapted to be deformed by the rapidly increasing pressure of combustion gases when a projectile is fired.

Another object of the present invention is the provision of a combustion gas responsive device for initiation projectile arming used in conjunction with a velocity sensitive receiver in the form of a primer such as a percussion primer, piezoelectric crystal, stab primer, or the like. c

These and further objects and advantages of the invention will be more apparent upon reference to the following specification, claims .and appended drawings wherein:

FIGURE 1 is a side view of a 40 millimeter cartridge with parts broken away to show the firing pressure activation system of the present invention;

FIGURE 2 is a simplified circuit diagram showing the detonator circuit for the cartridge of FIGURE 1;

FIGURE 3 is a perspective view of a percussion primer and associated structure incorporated in the cartridge of FIGURE 1;

FIGURE 4 is a cross sectional view of the pressure hammer and primer assembly as it appears prior to firing;

FIGURE 5 is a view similar to that of FIGURE 4 illustrating the deformation of the pressure hammer after the cartridge has been fired; and

FIGURE 6 is a perspective view showing the rear of the pressure hammer after firing.

Referring to the drawings, FIGURE 1 generally indi- Gates at 10, a cartridge comprising a metal casing 12 joined to a projectile 14. Cartridge 10 is of the 40 millimeter type and by way of illustration only incorporates a base mounted and pressure initiated electric impact fuze. Incorporated in projectile 14 as illustrated in FIGURE 2 is a battery 16, an arming switch 18, an impact switch 20 and detonator 22. Detonator 22 is connected across battery 16 in series with the switches 18 and 20 by the ground connections illustrated at 24 and 26. When the projectile 14 is fired, closure of switch 18 is initiated so as to arm the projectile. Impact of the projectile on its target causes impact switch 20 to close completing the circuit from the battery 16 to the detonator 22 to explode the cartridge at impact.

The system of the present invention is directed to the initiation of the closure of arming switch 18 of FIGURE 2 which initiation occurs subsequent to and as a result of the projectile 14 being fired. To better understand the invention, part of the casing 12 in FIGURE 1 has been cut away to show the novel pressure hammer and associated structure which acts to arm the switch in response to the combustion gas pressures within the casing 12.

Cartridge 10 of FIGURE 1 is illustrated as of the center fire type and to this end, the casing 12 is provided with a conventional primer 28 communicating with a first explosion chamber 30. By way of example only, the cartridge 10 may be of the type suitable for use in the M79 grenade launcher wherein the cartridge case is a high-low dual chamber type. Efiicient smokeless propellant combustion takes place in the central confined chamber 30 at a high pressure of about 35,000 p.s.i. The combustion gases are vented from chamber 30 through a burster diaphragm 32 by way of several annularly spaced passageways 34 into a larger chamber 36 at a lower pressure, for example, 3000 p.s.i. to propel projectile 14.

Threaded into the base 38 of the projectile 14 is a power supply and arming switch assembly 40 shown in more detail in FIGURE 3. Assembly 40 is provided .at its forward end with threads 42 for attachment to the projectile base and is provided at its rear end with a central aperture 44 in which is mounted a conventional percussion primer 46. By way of example only, primer 46 may be of the type designated by the military series M42 although a variety of other primers including both military and commercially available equivalents may be used. Although the invention is described specifically in conjunction with a percussion type primer 46 it is understood that the present invention is equally applicable to other type receivers or primers which require a high velocity or abrupt impact for them to initiate such as a well known piezoelectric (barium titanate, lead titanate, etc.), as well as the well known so-called stab primers. As is well known, all of these primers are of the type which are only actuated by an abrupt impact or contact from a striker and cannot be operated by a gradual increase in pressure resulting in a slow approach of the striker since the primer is simply crushed or destroyed under these circumstances without being actuated.

Energization of the primer is brought about by an .abrupt, sharp, or high velocity impact from a pressure hammer generally indicated at 50 in FIGURE 1 and illustrated in more detail in FIGURES 4 and 5. Referring to FIGURES 4 and 5, the power supply and arming switch assembly 40 comprises a lower end threaded at 42 for attachment to the base of the projectile 14, intermediate circular flange 52 and a rearwardly extending circular hub 54 which centrally mounts at its rear end primer 46 indicated by dashed lines in FIGURE 4. Spaced from the rear end 56 of hub 54 is .a circular disc 58 on which is mounted a striker 60. Disc 58 forms part of a cup 62 including a tubular portion 64 integral with the disc 58 and received with a friction fit over the outer end of hub 54. The tubular portion 64 of the cup is provided with a circumferential depression 66 to form an annular internal shoulder 68 which engages the outer end 56 of hub 54 to space disc 58 from the hub. If desired, shoulders 68 may be omitted and tubular portion 64 extended inwardly into engagement with flange 52 to provide proper spacing of the disc 58 from the hub. Striker 60 is in the form of a rivet passing through a suitable aperture in the center of disc 58 and carrying an integral hemispherical head 70 adapted to engage primer 46 when the disc is deformed by the pressure of the ginllqlaulstion gases in chamber 36 of the cartridge of FIG- FIGURE illustrates how the disc 54 is deformed by the pressure of the combustion gases to drive striker 60 and more especially hemispherical head 70 against primer 46 to initiate closure of arming switch 18 of FIGURE 2. The disc is formed of a suitable ductile metal such as gilding metal, copper, or the like which is sufficiently thin so it is abruptly dished inwardly and flows without any substantial resistance under the influence of the high pressures within the cartridge case as the projectile is fired. Impingement of hemispherical head 70 on the primer 46 energizes the primer which is coupled to the arming switch 18 and causes it to close the arming switch. This may be done in any of a variety of well known ways forming no part of the present invention and elaboration on the details of the arming switch are deemed unnecessary. In the preferred embodiment, heat generated by the primer closes the arming switch after a short delay. After a suitable time delay built into the projectile, arming switch 18 closes and the projectile is fully .armed so that it may be detonated by closure of impact switch at the time the projectile impacts on the target. Although described in conjunction with an electrical impact fuze, it is apparent that the pressure hammer .and primer combination may be used in conjunction with a wide variety of fuzes and with all types and sizes of projectiles. If desired, a suitable deformable cover (not shown) such as a metal barrier may be placed over primer 46 to hermetically seal the primer. In such a case, the cover barrier of metal is dented inward by the hemispherical head 70 of the striker to initiate the primer.

As previously mentioned, the device of the present invention is not limited to use with percussion primers but may be used with any high velocity responsive receivers including piezoelectric crystals, stab primers and the like. Likewise, while the deformable or ductile disc has been specifically disclosed as forming a part of a cup, it is apparent that the disc can be mounted in other ways and may, for example, be in the form of a flat circular disc which is peripherally restrained or clamped. The particular material from which the disc is formed is not critical and in addition to the materials previously described, other ductile metals such as aluminum, brass, and even steel may be used depending upon the size, pressures and other parameters of the system.

In the specific embodiment disclosed involving a 40 millimeter cartridge of the type shown, typical propulsion pressures generated by the combustion materials in the casing are in the neighborhood of 3000 to 3500 p.s.i. The cup 62 may be formed of a flat sheet of gilding metal or brass having a thickness in the range from 10 to 12 thousandths of an inch. By way of example only, in this specific embodiment, the disc may have a diameter of approximately W inch. The disc 58 may be initially spaced from the rear wall 56 of hub 54 by a distance of approximately thousandths of an inch. In this case, the initial spacing between the tip of head 70 and the primer 46 is approximately in the neighborhood of from 50 to 62 thousandths of an inch. The striker 60 may be formed of steel and riveted or soldered onto the disc 58. If used in conjunction with a stab type primer head 70 is preferably in the form of a conical point rather than the hemispherical shape more suited to percussion primers. The total weight of the pressure hammer including cup 62 and striker 60 is quite small, i.e., in the neighborhood of 10-15 grains or less.

The above are all given by way of example only and it is understood that various changes and modifications in materials, thicknesses, spacings and the like may be made over a broad range depending upon projectile sizes, pressures, temperatures and desired operation conditions. However, important features of the present invention include the provision of a very lightweight pressure hammer which, because of its low mass, is substantially insensitive to shock and vibration, and the combination of this hammer in the form of ductile metal which flows at a high velocity and with little resistance under the influence of a rapid buildup of pressure in the cartridge casing to impact a high velocity responsive receiver such as the percussion or like primer 46.

It should be noted that the friction fit afforded by the tubular portion 64 of the cup 62 has the advantage that it is quite leaky, i.e., permits leakage of air or gas into the space between the disc 58 and the back wall 56 of hub 54. Thus, should the projectile in which the pressure hammer is mounted be subjected to increasing temperatures, no large pressure buildup will take place behind disc 58 which might tend to drive striker 60 into the primer 46. That is, any pressure differential across the diaphragm will be immediately relieved by leakage between the walls of the cup and the hub 64 in such a direction .as to equalize any heat induced pressure buildup across disc 58 such as might occur if the cartridge or the weapon in which it was placed should be in or near a fire. For example, excessive pressures in chamber 36 due to the heat from a fire or other causes would not cause the disc 58 to deflect due to this leakage but rather would first leak out of casing 12 around the projectile 14 before having any adverse effect on the pressure hammer.

The invention may be embodied in other specific What is claimed and desired to be secured by United States Letters Patent is:

1. A combustion gas responsive actuator for fuzes and the like comprising:

(a) a disc of ductile metal forming part of a metal cup and supported around its periphery;

('b) a percussion primer insensitive tofilow velocity shocks and mounted in a housing, said metal cup having its open end received over said housing with a friction fit and including an annular indentation in said cup forming an internalshoulder engaging said housing to space said disc from said primer; 2

(c) .a striker carried at the center of said disc whereby deformation of said disc by combustion pressures causes said striker to engage said primer at a high velocity;

(d) a cartridge including a casing and projectile, said disc and primer being mounted in the combustion chamber of said cartridge between said casing and said projectile;

(e) fuzing means including a battery, an arming switch responsive to thermal energy generated by said primer, impact switch and detonator in said projectile, said switches being connected in series with said detonator across said battery, said primer being coupled to said arming switch' to initiate closure of said arming switch. I

2. The actuator of claim 1 wherein the total weight of said disc and striker is no greater than about 15 grains whereby said actuator is substantially insensitive to shocks and vibration.

References Cited UNITED STATES PATENTS 2,462,305 2/1949 Catlin 102--81 X 2,627,810 2/1953 Catlin 10270 2,737,892 3/1956 Dalton et a1. 102--81 2,798,921 7/1957 Haas 10270.2 2,873,681 2/1959 Lauritsen 10281 2,982,213 5/1961 Meschino et a1. 10270.2 3,262,387 7/1966 Realms 102-81 X BENJAMIN A. BORCHELT, Primary Examiner. GERALD H. GLANZMAN, Assistant Examiner.

US. Cl. X.R 

